Automatic transmissions, particularly for motor vehicles, comprise planetary gear sets according to the prior art that are engaged by means of friction or shift elements such as clutches and brakes and are typically connected to a startup element, such as a hydrodynamic torque converter or a hydraulic coupling, subject to a slip effect and optionally equipped with a lock-up clutch.
Such type of automatic transmission is known, for example, from DE 199 12 480 B4 of the applicant. It comprises three carrier planetary gear sets as well as three brakes and two clutches for engaging six forward gears and one reverse gear, one drive shaft and one output shaft, in which the carrier of the first planetary gear set is permanently connected to the ring gear of the second planetary gear set and the carrier of the second planetary gear set is permanently connected to the ring gear of the third planetary gear set and the drive shaft is directly connected to the sun gear of the second planetary gear set.
Furthermore, with the known transmission, it is provided that the drive shaft can be connected to the sun gear of the first planetary gear set via the first clutch and can be connected to the carrier of the first planetary gear set via the second clutch, in which the sun gear of the first planetary gear set can be connected to a housing of the transmission via the first brake and the carrier of the first planetary gear set can be connected to the housing of the transmission via the second brake, in which the sun gear of the third planetary gear set can be connected to the housing of the transmission via the third brake. The output shaft of the transmission is permanently connected to the carrier of the third planetary gear set and the ring gear of the first planetary gear set.
Furthermore, a 9-gear multi-stage transmission is known from DE 29 36 969 A1; it comprises eight shift elements and four planetary gear sets, in which one planetary gear set serves as a front-mounted transmission and the main transmission has a Simpson set and a planetary gear set serving as a reverse gear.
Further multi-stage transmissions are known, for example, from DE 10 2005 010 210 A1 and DE 10 2006 006 637 A1 by the applicant.
Vehicle transmissions in a planetary design that can be shifted automatically have already generally been often described in the prior art and are subject to continuous further development and improvement. Thus, these transmissions should require lower construction costs and a smaller number of shift elements and, when there is sequential shifting, prevent double shifting operations, i.e. the engagement and disengagement of two shift elements, which means that only one shift element is shifted when there are shift operations in defined groups of gears.
DE 10 2008 000 428 A1 from the applicant states that a multi-stage transmission in a planetary design is known, having one drive and one output, which are arranged in a housing. With the known transmission, at least four planetary gear sets, which are designated in the following as the first, second, third, and fourth planetary gear sets; at least eight rotatable shafts, which are designated in the following as the drive shaft, output shaft, third shaft, fourth shaft, fifth shaft, sixth shaft, seventh shaft, and eighth shaft; as well as a least six shift elements, comprising brakes and clutches are provided, the selective engagement of which effects various transmission ratios between the drive and the output, which means that preferably nine forward gears and one reverse gear can be implemented.
In this case, the first and the second planetary gear set, which are preferably implemented as minus planetary gear sets, i.e. with negative stationary transmission ratios, form a splitter gear set which can be shifted and in which the third and the fourth planetary gear sets form a main gear set.
With the known multi-stage transmission, it is provided that the carriers of the first and the second planetary gear sets be coupled with one another via the fourth shaft, which is connected to an element of the main gear set, that the ring gear of the first planetary gear set be coupled to the sun gear of the second planetary gear set via the eighth shaft, which may be detachably connected to the drive shaft via a first clutch, and that the sun gear of the first planetary gear set be coupled to a housing of the transmission by means of the third shaft via a first brake and be detachably connected to the drive shaft via a second clutch, in which the ring gear of the second planetary gear set may be coupled to a housing of the transmission by means of the fifth shaft via a second brake. In addition, the seventh shaft is permanently connected to at least one element of the main gear set and may be coupled to the housing of the transmission via a third brake, in which the sixth shaft is permanently connected to at least one further element of the main gear set and is detachably connected to the drive shaft via a third clutch; the output shaft is permanently connected to at least one further element of the main gear set.
It is preferable with the known transmission if the fourth shaft is permanently connected to the ring gear of the third planetary gear set, in which the sixth shaft is permanently connected to the ring gear of the fourth planetary gear set and the carrier of the third planetary gear set and is detachably connected to the drive shaft via the third clutch. Furthermore, the seventh shaft is permanently connected to the sun gears of the third and fourth planetary gear sets and may be coupled to a housing of the transmission via the third brake. The output in this case takes place via the output shaft permanently connected to the carrier of the fourth planetary gear set. Furthermore, the third and the fourth planetary gear sets may be combined or reduced to a Ravigneaux set with a shared carrier and a shared ring gear.